Oxidation of cobaltous chloride ion to the cobaltic ammine ion is accomplished in an ammoniacal-ammonium chloride solution in the presence of an activated charcoal catalyst. The reaction mixture is essentially buffered at a pH of from about 9.0 to about 9.4. After a period of aeration, &gt;98% by weight of the Co ions have been oxidized to Co(NH.sub.3).sub.6.sup.3+. Much of the Co at this point precipitates as [Co(NH.sub.3).sub.6 ]Cl.sub.3 due to the initial high concentration of chloride ion. However, in order to recover &gt;98% by weight of the cobalt as the solid ammine complex additional chloride ion must be added to the mixture. At the present time, HCl is used as the source of chloride ion. This is described in U.S. Pat. No. 4,612,039. Hydrochloric acid is added to a pH of about 0.5 at which &gt;98% by weight of the cobalt can be recovered by way of filtration. (The solid hexammine compound is further processed to extra fine cobalt metal powder.) The mother liquor from this filtration can contain up to about 5% of the initial cobalt (although generally about 2% or less) and, therefore, is treated in a separate step to recover the cobalt. This is accomplished by raising the pH to 8.0 to 8.5 with NH.sub.4 OH and then cementing the cobalt out of solution with aluminum metal powder. After the cobalt is removed, the liquor is sent to a steam stripper for ammonia recovery. The recovered cobalt is then redigested in HCl and recycled to the beginning of the process. In the above process, much acid and ammonia are consumed. This results in high cost for materials and for extra processing.
Therefore, a process in which less acid and ammonia are used would be advantageous both from an economical and an environmental standpoint.
The following U.S. Patents relate to cobalt processing:
U.S. Pat. No. 4,184,868 relates to a method for producing extra fine cobalt metal powder by digesting cobalt pentammine chloride in ammonium hydroxide to obtain a black precipitate which contains cobalt and which is thereafter reduced to metal powder. U.S. Pat. Nos. 4,214,894, 4,214,896, 4,233,063, and 4,278,463 relate to improvements in U.S. Pat. No. 4,184,868 in which the ammonia solutions are processed to recover any cobalt therein. U.S. Pat. Nos. 4,395,278 and 4,469,505 relate to improvements in U.S. Pat. No. 4,184,868 in which fine cobalt metal powder is 10 produced having reduced tailings.
U.S. Pat. No. 4,214,895 relates to a process for producing cobalt metal powder which involves treating an aqueous solution of a soluble cobaltic ammine halide with a sufficient amount of a soluble metallic hydroxide to form a cobalt containing precipitate which is thereafter reduced to metallic cobalt.
U.S. Pat. Nos. 4,218,240 and 4,690,710 relate to methods for producing cobalt metal powder by forming a solution of a cobalt hexammine compound and treating the solution with a metallic hydroxide to form a precipitate which is reduced to cobalt metal powder. U.S. Pat. Nos. 4,348,224 and 4,381,937 relate to improvements in the process described in U.S. Pat. No. 4,218,240 which involve removal of copper and silver from the cobalt. U.S. Pat. No. 4,452,633 relates to an improvement in the processes described in U.S. Pat. Nos. 4,218,240 and 4,348,224 in which the silver is recovered.
U.S. Pat. No. 4,612,039 relates to a process for recovering cobalt in which cobalt is first reduced to the metal followed by ammonia-ammonium chloride digestion to form an hexammine cobalt (III) chloride while hydrochloric acid is added to precipitate the hexammine cobalt (III) chloride. The mother liquor is therefore acid and ammonium hydroxide is required to raise the pH to further recover any cobalt which remains in the mother liquor.
U.S. Pat. Nos. 4,608,084 and 4,608,235 relate to processes for recovering cobalt from stellite material.
U.S. Pat. No. 4,606,885 relates to producing a pure cobalt article.
U.S. Pat. No. 4,594,230 relates to a process for recovering cobalt from cobalt material by digestion in hydrochloric acid followed by precipitation of cobalt oxalate.
U.S. Pat. No. 4,578,251 relates to a process for separating chrominum from cobalt.
U.S. Pat. No. 4,093,450 to Doyle et al describes a process for producing fine particle size cobalt metal powder by the hydrogen reduction of cobalt oxide obtained from a cobalt pentammine carbonate solution. The precipitate is formed by heating the solution to drive off ammonia and carbon dioxide to form a precipitate of cobalt oxide.
U.S. Pat. No. 4,329,169 relates to a process for producing fine cobalt metal powder absent tailings by heating an aqueous solution of soluble cobalt ammine halide to decompose the halide and form a cobalt containing precipitate which is reduced to the cobalt metal powder.
U.S. Pat. No. 4,409,019 relates to a process for producing fine cobalt metal powder from pieces of relatively pure cobalt by dissolving the cobalt pieces in an aqueous solution of hydrogen iodide and iodine and forming a cobalt containing solid which is subsequently reduced to a fine cobalt metal powder.